1. Field of the Invention
This invention is directed to rubber-rubber composite structures obtained by the unique bonding of preforms formed from specific rubber compositions.
2. Description of the Prior Art
As is generally known, rubber compositions containing hydrogenated acrylonitrile-butadiene rubber, methacrylic acid, zinc oxide and an organic peroxide are colorable in any desired colors and, upon vulcanization, are not only resistant to heat and to oil, impermeable to gas and weatherable but also mechanically strong, hard, elastic, stretchable and low in specific gravity. If it is made possible to bond by vulcanization an unvulcanized preform formed from such a rubber composition directly onto a similar preform formed from a rubber composition containing a rubber in common use, then a composite structure of rubber-to-rubber bonding will be produced which is blessed with physical characteristics peculiar to the two different rubber compositions. The composite structure thus obtained is expected to be suitable particularly for use as a material for belts, hoses, pneumatic tires and the like. For instance, weight saving has been more and more strict with respect to pneumatic tires in the automobile industry. This trend will be coped with by the use of the above rubber-rubber composite structure if the latter can be employed to partly or wholly form a bead filler, an inner liner, a tread portion and the like for the tire.
Even regardless of physical properties of the ultimate composite structure, it is very difficult to bond, with use of a conventional adhesive for rubber, a preform resulting from a rubber composition containing hydrogenated acrylonitrile-butadiene rubber, methacrylic acid, zinc oxide and an organic peroxide onto a preform resulting from a rubber composition containing a general-purpose rubber. An adhesive of an isocyanate resin or epoxy resin type would make the resulting bonded layer brittle and hence susceptible to failure only under appreciable deformation. The first- and last-mentioned preforms, therefore, are required to be bonded together by vulcanization or in any other way without reliance on a resin type adhesive.